There are many sample preparation methods used today. For example, electrophoresis is a widely used method for sample preparation of proteins and peptides. The sample may be separated in 1 dimensional or 2 dimensional electrophoresis, wherein 1D electrophoresis separates molecules on the basis of e.g. pI-value and 2D electrophoresis includes an additional separation according to size and possibly charge. For sample preparation, electrophoresis is cumbersome and time consuming. Another drawback is that the sample has to be eluted from the gel if it is desired to use or analyse the sample further.
Another example of sample preparation is liquid chromatography which may be used as 1D, 2D or MDLC (multi dimensional liquid chromatography) separation. The liquid chromatography may be sieving chromatography, ion exchange chromatography, hydrophobic interaction chromatography, affinity chromatography etc. The drawback with liquid chromatography is that it is less suited for handling very small amounts of sample. The limitation in handling small amounts of sample with chromatographic methods is in part overcome by using so called micro spin columns.
Other techniques that are currently in use for sample preparation of very small sample amounts make use of pre-coated microtiter plates. These plates can be prepared with ligands that can remove bulk impurities as well as be used for specific isolation of target components.
Yet another sample preparation approach is based on the use of magnetic beads. Magnetic beads are also available with ligands suited for removal of bulk proteins or isolation of specific target components. These materials are commonly handled in test tubes in combination with a manual pipetting procedure.
Various types of microfluidic systems have also been described for sample preparation and other manipulations (see e.g. P E Andersson: PharmaGenomics (2), 38-44 (2003)). A drawback in many of these is that the macro/micro interface becomes inconvenient, i.e. the transfer of a macroscopic (microliter/milliliter) sample into channels of nano/picoliter dimensions is a weak spot in the system. Further, they are often not well suited for handling small amounts of particulate materials.